The invention relates generally to computer touchscreens, and more particularly, to electrically conductive materials for touchscreens.
Since their introduction in the early 1970s, touchscreens have afforded alternatives to keyboards for certain computer applications. In many situations the keyboard and mouse are eliminated, because the touchscreen provides the user with access to the computer. Both resistive and capacitive touchscreens typically include a substrate, such as a glass panel, that is positioned over the face of a display, for example a liquid crystal display (LCD). The substrate includes an electrically conductive material on a surface thereof. The electrically conductive material defines an electrically conductive touch area on the substrate surface for accepting a user's inputs to the touchscreen. An insulating layer is positioned over the electrically conductive area to provide a surface for the user to touch to select the inputs.
In a resistive touchscreen, the insulating layer forms a portion of a cover sheet that includes a second electrically conductive material located over a surface of the insulating layer facing the substrate. The cover sheet is spaced from the substrate by a plurality of insulating dots such that the two electrically conductive materials are spaced apart. When the cover sheet is touched by a user, the two electrically conductive materials engage each other at the location of the user's touch. In capacitive touchscreens, the insulating layer is deposited directly on the electrically conductive material on the substrate.
The electrically conductive materials on both the substrate and the insulating layer are typically formed from indium tin oxide (ITO). ITO is often used because ITO generally provides good transparency for a given value of electrical conductivity, as is desired for some touchscreen applications. However, ITO may be somewhat brittle such that the electrically conductive material may crack, fracture, and/or fatigue after repeated touches, which may cause the touchscreen to malfunction, fail, and/or function differently than intended. Moreover, because the supply of indium is limited, ITO may be relatively expensive. Increasing demand for indium may cause ITO to become even more expensive as the world supply diminishes.
To replace ITO, metal nanofibers have been proposed for use in the electrically conductive material that is present on the substrate and/or on the cover sheets of touchscreens. However, metal nanofibers may be prone to atmospheric corrosion. Atmospheric corrosion of metal nanofibers within the electrically conductive material may increase a contact resistance of the electrically conductive material, which may decrease the flow of electrical current into and out of the electrically conductive material at the point of contact between the electrically conductive material with another electrically conductive material. Carbon nanotubes have also been proposed as a replacement for ITO in the electrically conductive material that is present on the substrate and/or on the cover sheets of touchscreens. However, carbon nanotubes may not match the transparency of ITO for a given electrical conductivity.
There is a need for an electrically conductive material that has an increased durability as compared with electrically conductive materials formed from ITO. There is also a need to improve the corrosion resistance of electrically conductive materials that include metal nanoparticles. Moreover, there is a need to improve the transparency of electrically conductive materials that include carbon nanoparticles.